Efforts to provide the benefits of immunization to the world's children have reached an important crossroad. While remarkable progress has been achieved in successfully administering six important childhood vaccines (diphtheria, tetanus, polio, pertussis, measles, and tuberculosis), the benefits of new vaccines, such as hepatitis B and Haemophilus influenzae type B glycoconjugate vaccines, have not been realized except in the most developed countries. The three reasons often cited to explain this problem include poor access to immunization services, the evolution of complex primary immunization schedules, and the additional expense associated with new vaccines, potentially depleting scarce resources. The establishment of the Children's Vaccine Initiative is an organized effort to improve immunization by both technological and organizational innovation. Simplification of the vaccination process can be achieved by developing new combination vaccines or reducing the number of immunizations with vaccines that stimulate protective immune responses. Improvements in the organization of efforts to immunize children will also enhance the prospects of protecting the world's children from infectious diseases. To achieve the goals articulated in the Declaration of New York, the issues of transition from the old to the new vaccines must be addressed. Research on vaccines and technological innovation at all levels will be required to achieve these goals.